Water-based inkjet inks are primarily used in inkjets of the
type standard and thermal. In this type of inks there is presence of
volatile organic compounds (VOC) and they do have low level of toxicity,
the dry rate is relativey slow on the non-absorbent substrates. They
often require a special coated media for optimizing dot gain and drying.
They also need lamination to secure water resistance. Originally they
were developed for the desktop systems only but moved on to facilitate
the growth of inkjet in wide-format graphics.
Of late there is a trend for the inkjet inks to become pigment based.
If we analyses the reasons for the spurt in popularity in the application
of pigment in inkjet inks the answers would not be very difficult to
understand. Pigments give environmental friendly products along with
durability and better compatibility with packaging. However one thing
needs to be specified here is that the colloidal properties generally
associated with pigments are more complex than dyes.
(For use in Achromatic Inks)
To make the white inks, the most important inorganic pigment is
Titanium dioxide. Another popular inorganic pigment, calcium carbonate
is used as an extender to make white inks. But, if we want to make black
ink, then the most randomly used inorganic pigment is carbon black.
We can therefore say that the inorganic pigments that are used for
making printing inks are Carbon Black (very important), Titanium Oxide,
Molybdenum Red Pigments and iron Blue all with medium usages while
Chromate Pigments (sparingly used).
(For use in Colored Inks)
Now a days, the inorganic colored pigments are very rarely used
because, these pigments contain very high degree of metallic toxics like
chromium, cadmium and lead. In their place to create green and blue
shades, phtalocyanine pigments are used. For red and yellow shades inks,
Azo pigments are very preferred medium.
Whether the molecules of the pigments will absorb light in the visible
range or not, depends upon the presence of the conjugated system of
double bonds in these molecules.
Advantages of pigment based inks are:
Pigments are tiny combinations of a variety of molecules. They are much
bigger in size than their dye counterparts. This size advantage
- Less susceptibility to environmental factors and oxidising gases.
Particles that are found in a dried pigment ink has a surface that is
very rough. As a result the light that is reflected of the prints has a
predominant tendency toward scattering, giving rise to colour that is
less saturated and dull.